This invention relates to an improvement on a ball joint, and more particularly to a heat resisting ball joint used in automotive steering and suspension systems for vehicles.
In general, a ball joint in which a spherical member or ball element for a ball stud is held in a preloaded condition within a resilient bearing accommodated in a housing, has been well known to the art.
A ball joint of this class heretofore found has been of one type, as typically disclosed in U.S. Pats. Nos. 2701151 or 2823055, that is a so-called "steel on steel" in which a bearing consists of a plurality of metallic elements or sintered alloy elements, and of the other type, as typically shown in U.S. Pat. Nos. 3073634, 3363921, and 3413023, that is a so-called "polymeric lined" in which a bearing consists of a single or plurality of synthetic resin or rubber members.
In a ball joint of the steel-on-steel type, it is practical to employ a coil spring and a specific metal hardening treatment in combination with a grease nipple for lubrication in order to compensate for wear on a contact surface or to relieve impact since such a ball joint construction will require a contact between a spherical member of ball element for stud and a bearing, namely, metal and metal. Although such construction is solid and durable, it requires complicated component.
A ball joint of the polymeric-lined type has proven satisfactory, and it eliminates not only the coil spring used for wear compensation and impact relief but also the need for a grease nipple, because the permanently lubricating structure of a ball joint using synthetic resin, rubber and a bearing structure properly preloaded has a low fiction coefficient. However, this type of ball joint is inferior to a metallic structure in rigidity, durability, and heat resistance.
Ball joints are subjected to critical environment conditions. For instance, ball joints for steering or suspension systems arranged adjacent the highly heated zone which is composed of a thermal reactor and catalyzer in the exhaust line of a non-pollution car engine are heated to a temperature of 120.degree. - 130.degree. C. Under this condition, ball joints which rely on contact between metals tend to run out of lubricant or the lubricant deteriorates and then the bearing surface becomes seizured when the dust cover is subjected to a high temperature or damage due to any other reason. This is entirely because of the structure which is adapted to distribute the lubricant between the dust cover and the bearing surface.
On the other hand a ball joint bearing of synthetic resin or rubber is lower in resistance to heat, and if such a ball joint is subjected to a high temperature, it softens and is deformed or melts and flows out of the space between the metal housing and ball stud spherical member or ball element to lessen the pre-load on the bearing.